Huge earthquake changed Earth’s gravity
06 December 2013
Although ESA’s GOCE satellite burned up during re-entry into Earth’s atmosphere a few weeks ago, this unique mission keeps on springing surprises. The latest unexpected discovery is that GOCE detected a marked change in the local strength of gravity after the massive earthquake that struck Japan in 2011.
Shaped like an arrowhead, GOCE was specially designed to create the most detailed and accurate map of variations in Earth’s gravity field ever made. As it flew along a near-polar orbit, the path of the streamlined satellite was altered slightly by changes in the planet’s gravitational pull.
Careful analysis of the data sent back by GOCE during its four year mission has enabled scientists to produce a remarkably accurate model (known as the ‘geoid’) of Earth’s gravity. However, the remarkable sensitivity of its gradiometer instrument also made it possible to study other features of our planet, such as ocean currents, changing sea level, land surface height and layers in Earth’s rocky crust. It even detected winds in space and sound waves that travelled up through the atmosphere after the huge Japanese earthquake on 11 March 2011.
Now GOCE has surprised everyone again by detecting changes in the local gravity field after the same magnitude 9 earthquake that devastated much of Japan. German and Dutch scientists have analysed the GOCE results and discovered that the quake clearly altered the strength of gravity on the island of Honshu and the nearby ocean floor. This is the first time that GOCE data have revealed changes over time.
In addition, the size and location of the gravity changes measured by GOCE are different from the predictions. By combining GOCE data with information from the German-US GRACE mission and other sources, scientists will obtain a much more accurate picture of what happened during the underwater quake.
